The present invention relates to an electromechanical switch, and more particularly to a switch, a filter, and a communication apparatus used for switching high frequency signals in a high frequency circuit in a mobile communication terminal, and used in digital television broadcasting, mobile phone and wireless LAN.
A conventional RF-MEMS switch is a mechanical switch in which a movable element formed into a membrane or rod shape is fixed at both ends or only at one end thereof so as to be brought into contact with or separated from an electrode to thereby switch propagation paths of signals. While in many publications, electrostatic force is used as a source of force actuating the membrane and the movable element, magnetic force is also used in many other publications as the source of such actuating force.
As a minute switch of a size in the order of 100 μm, there is conventionally known one described in Non-Patent Document 1. The configuration of the conventional switch described in Non-Patent Document 1 is shown in FIGS. 22A and 22B. FIG. 22A is a sectional view showing the configuration of the conventional switch, and FIG. 22B is a plan view showing the configuration of the conventional switch. FIG. 22A is the sectional view sectioned along the line A-A′ in FIG. 22B. In this switch, a signal line 1 along which a high-frequency signal is transmitted is formed on a membrane, and a control electrode 3 is provided directly below the signal line 1.
When a direct current potential is applied to the control electrode 3, the membrane is pulled towards the control electrode 3 by virtue of electrostatic pulling force and is then deflected to be brought into contact with a ground electrode 4 formed on a substrate 2. As a result, the signal line 1 formed on the membrane comes into a short-circuited state, and the signal flowing through the signal line 1 is attenuated to be cut off.
On the other hand, when the direct current potential is not applied to the control electrode 3, the membrane is not deflected. The signal flowing through the signal line 1 on the membrane from the ground electrode 4 passes through the switch with no loss.
[Non-Patent Document 1]
IEEE Microwave and Wireless Components Letters, Vol. 11 No. 8, August 2001 p 334
As properties of the electromechanical switch, it is necessary to ensure isolation when the switch is off as well as reduce pull-in voltage necessary for switching operations.
In the conventional electromechanical switch, however, when a configuration is adopted in which the gap is increased to ensure the isolation, resulting in a large displacement, there is caused a problem that the pull-in voltage necessary for switching operations has to be increased, Conversely, when a configuration is adopted in which the gap is decreased to reduce the pull-in voltage, there is caused a problem that the isolation is reduced when the switch is off. Thus, the actuation with the low voltage and the isolation characteristic are in an incompatible or trade-off relationship.